Sure, but what's good for an individual person is not always suitable for a state or large organisation. It's hard to imagine that private key(s) to an entire nation's bitcoin investment would be held either by a single official or a group of officials (for multisig wallets). Government employees are not famous for being too security-focussed or for taking their roles seriously. They probably wouldn't want such responsibility anyway.
So, in this case, using a trusted, centralised service, with all the insurance etc, seems perfectly justified.